He spoke of the spirit we need to move forward in the next four years, next 40 years, the next 400 years.

He spoke of a call to action, of the oath we all take, of the power we have as citizens to "shape the debates of our time ... to answer the call of history."

His words echoed those of John F. Kennedy's famous inaugural address.

Obama has changed in the four years since he was first sworn in as president. The nation that elected him again also has changed.

The economy is in better shape, but we face many important and divisive issues, from gun control to health care to immigration to economic equality to climate change to our role overseas.

He made little mention of the deficit and federal debt, which also pose vexing political challenges.

How we address these issues and more will say much about what our future will hold.

He challenged us to work together, even when we don't agree on every detail.

At times he was speaking directly to Congress and the elected leaders he will have to work with for four more years. "We cannot mistake absolutism for principle."

That is one of the most important points he made on Monday before a throng of 800,000.

He spoke of the Constitution and how our collective allegiance to its ideal is what makes us Americans. "That all men are created equal. That they are endowed by their creator with certain inalienable rights. Among these are life, liberty and the pursuit of happiness.

"Today we continue a never-ending journey, to bridge the meaning of those words with the realities of our time. For history tells us that while these truths may be self-evident, they've never been self-executing."

He spoke of our love and celebration of initiative, from the Founding Fathers to today. He said we have "never relinquished our skepticism of central authority nor have we succumbed to the fiction that all society's ills can be cured through government alone."

He kept returning to the theme that we also need to take care of the most vulnerable in our society and that we need to work together, collectively as one nation, to keep us strong and just. He kept reminding us that opportunity and equality are inextricably linked.

He said the future is bright. The possibilities limitless. The challenges great.

President Obama is right on all three counts. He is right that we must put aside our differences, whenever possible, and work together; that we must honor the past but recognize that changing times require fresh ideas and approaches.

That is easier said than done. But if we don't try, we will not succeed.